There are biochemical differences in the brains of men and women determining their behaviour

The argument

Proponents of this position argue that the development of the brain follows a separate timetable from the development of the body, and that this separation is where the biological account of gender begins. Sexual differentiation of the genitalia takes place within the first two months of a pregnancy. The sexual differentiation of the brain begins only in the second trimester, and on this account it is testosterone that determines whether the brain develops along male or female lines. The two processes are therefore distinct events, and proponents hold that the later one shapes behaviour, sexual orientation and gender identity. The evidence they point to is structural. Differences in the hypothalamus are offered as showing the variation directly: the preoptic area, which regulates mating behaviour, is said to be 2.2 times larger in males and to contain twice as many cells, with the difference depending on the number of androgens present during development. This is presented as a physical difference of a measurable kind rather than an inference drawn from observed behaviour. The developmental timing is treated as significant in itself. Proponents note that these differences become apparent at around the age of four, and that after that age the number of cells in this nucleus decreases in females. The pattern is taken to indicate a biological process unfolding on its own schedule, rather than one produced by the accumulating social expectations placed on a child. Because the differences are said to arise from prenatal hormones and to shape functions and sexual preferences thereafter, proponents argue that the traits in question are determined biochemically rather than assigned socially — and therefore that gender is not a social construct.

Premises

Counter-arguments

It is averred that the differences in the brain are negligible as there are no significant differences based on sex alone. This distinction between the male and female brain seems to suggest that all males think and operate on one level and all females think and operate on another. There are variations and differences in thinking, aptitudes and personalities, which need to be considered. The biological distinction between a male and female can actually be harmful as it suggests that one gender may not have the aptitude for something that the other has, when that is simply not the case.

Rejecting the premises

[Rejecting P1] Prenatal androgen exposure influences how some brain structures develop, but the premise slides from influence to determination — and "develops as a male or female brain" treats a set of overlapping continuous measurements as two discrete kinds. [Rejecting P2] Group averages do not describe individuals: the reported differences are means with wide overlapping distributions, so a person's sex does not predict their measurements, and the structure named regulates particular functions rather than behaviour in general. [Rejecting P3] The strongest claim is the least supported. No established finding shows these structures determining gender identity or sexual orientation, and even a wholly biological account of a trait would not settle whether the social expectations attached to it are constructed — which is what the question asks.